1. Technical Field
This invention generally relates to fluid content sensors. More particularly, this invention relates to a sensor arrangement having a single capacitor that is used in two different modes to determine desired characteristics of a fluid mixture that is used to provide hydrogen to a fuel cell, for example.
2. Description of the Prior Art
A variety of sensors for determining fluid contents are known. Fuel sensors, for example, typically are used to determine the content of a fuel mixture within a fuel system of a vehicle. Some sensors are capable of determining the content of the fuel mixture such as a ratio or proportion of alcohol to gasoline within the fuel. Depending on the determined ratio, the ignition timing and fuel quantity supplied by fuel injectors may be adjusted by a suitable fuel flow control system.
It is known that the relative permittivity and conductivity of substances or fluids differ from each other because of the different oxygen levels within each, for example. Accordingly, the relative contents of a fluid mixture of known components may be a well-defined function of the fluid's relative permittivity, temperature and conductivity.
Known sensors take advantage of these known characteristics and utilize the electrical properties of the fluid mixture contents to make a determination regarding concentrations, for example. Sample patents in this field of endeavor that are directed toward fuel systems include U.S. Pat. Nos. 4,945,863 and 5,367,264. Each of these patents show approaches to providing a fuel sensor that utilizes the electrical properties of the fluid for making fuel content determinations.
While the current approaches have proven satisfactory, those skilled in the art are always striving to make improvements. For example, alternative power sources for vehicles, such as fuel cells, have particular measurement requirements. Additionally, packaging constraints on vehicle systems continuously cause an emphasis to be placed upon minimizing the size of components and maximizing the convenience of integrating them into vehicle systems. Additionally, cost savings are always a concern to automotive suppliers.
This invention addresses the need for providing an economical and convenient approach to measuring properties of a mixture used to provide fuel such as hydrogen to a fuel cell.